The present disclosure relates to radiographic imaging and in particular to an apparatus and method for positioning two bi-plane imaging systems that facilitates three-dimensional measuring of in vivo joint kinematics.
Cartilage is the part of the joint that cushions the ends of the bones and allows joints to move freely. Osteoarthritis (OA) is considered to be one of the most common forms of arthritis. OA is referred to in the medical industry by many different names, including degenerative joint disease, osteoarthritis, hypertrophic arthritis and degenerative arthritis. Generally, OA refers to a chronic condition portrayed by the breakdown of the cartilage within a joint. The breakdown of cartilage causes friction between the bones, causing stiffness, pain and loss of movement in the joint.
Today, it is estimated that over 20 million Americans are plagued by the effects of OA. Additionally, OA accounts for approximately a quarter of visits to primary care physicians as well as about half of all non-steroidal anti-inflammatory drugs (NSAID) prescriptions. It has been estimated that over 75% of the population can have radiographic evidence of OA by the age of 65, although only 50-60% of those can be symptomatic. Most often, treatment is with NSAIDs, local injections of glucocorticoid or hyaluronan. In severe cases, patients can undergo surgery with joint replacement or fusion.
Despite the disease's prolonged existence and rate of recurrence, its cause is still not completely known by the medical industry. As such, there is no cure. However, it is believed that there are a number of defined factors that contribute to OA. These factors include enhanced age, obesity, injury, overuse and genetics.
As with many diseases, there are several stages in which the body (and joints) undergo. First, cartilage can lose elasticity which inherently makes it more easily damaged by injury or overuse. Another stage occurs when the wear of the cartilage causes changes to underlying bone. When this occurs, the bone can thicken and cysts may occur under the cartilage. Spurs or osteophytes develop near the end of the bone at the affected joint. This breakdown of the cartilage can cause bits of bone or cartilage to ‘float’ loosely in the joint space. As a result, the joint lining, or the synovium, usually becomes inflamed due to cartilage breakdown causing cytokines (or inflammation proteins) and enzymes that further damage cartilage.
Essentially, changes in the cartilage and bones of the joint can lead to pain, stiffness and range of motion limitations. Deterioration of cartilage can affect the shape and makeup of the joint thereby prohibiting or impairing ‘normal’ function. In other words, deterioration of cartilage in a knee or ankle joint can cause a person to limp. As well, in a more extreme case, fragments of the bone and/or cartilage can ‘float’ within the joint. Here, the person can experience pain when putting weight on the joint (e.g., standing, walking, ascending/descending stairs, etc.). As the bone surfaces become less protected by cartilage, a patient can experience pain upon weight bearing. Due to decreased movement because of the pain, regional muscles may waste away or atrophy.
OA (and other joint impairment) diagnosis is normally accomplished via imaging techniques or X-rays. This is possible because loss of cartilage, narrowing of the joint space between the bones, and bone spur formation (aka osteophytes) can be easily detected by way of X-rays. With or without other techniques, such as MRI (magnetic resonance imaging), arthrocentesis and arthroscopy, diagnosis can be made by a careful study of the duration, location, the character of the joint symptoms, as well as, the appearance of the joints themselves. Unfortunately, to date, there are no reliable and effective mechanisms available to detect OA in its early and potentially treatable stages.
Conventional approaches for measuring three-dimensional (3D) joint position and motion have relied upon cadaveric simulations, two-dimensional (2D) imaging, static 3D imaging, conventional motion measurement systems, and invasive techniques using bone pins. Unfortunately, there are significant limitations associated with each of these approaches. Cadaveric experiments can provide highly accurate measures of joint position or motion, but are unable to accurately duplicate the complex motions, muscle forces, or joint forces associated with dynamic in vivo conditions. Joint position has been evaluated radiographically, using fluoroscopy to measure dynamic joint motion or plane films to measure static joint position. However, these 2D assessments of joint motion cannot sufficiently characterize motion of a joint that is capable of translating in three directions and rotating about three axes. Static 3D imaging of joint position has been performed with magnetic resonance imaging, CT, or biplane radiography, but these techniques are currently incapable of assessing dynamic joint motion. Conventional motion measurement systems have used video cameras to measure the position of surface markers or anatomical landmarks or have relied on surface-mounted electromagnetic motion sensors. Combinations of the aforementioned approaches are also used, with Barnett and colleagues describing the combined use of a surface-mounted scapular locator, electromagnetic device, and optical motion tracking system. Skin-mounted sensors are highly susceptible to skin movement artifact, and their reliability for the accurate assessment of joint kinematics has not been established. Invasive techniques using bone pins have been used by McClure and colleagues to directly measure scapular motion of eight volunteers. However, this invasive approach not only limits the number of willing volunteers, but also makes serial studies over time impractical since bone pins cannot be reliably secured in the same location. More recently, our laboratory has begun using dynamic radiostereometric analysis (RSA) to measure 3D joint kinematics by tracking the position of implanted tantalum beads with a novel, high-speed, biplane X-ray system. This approach has been used extensively to study in vivo knee kinematics in canines and humans. However, tantalum marker implantation is an invasive procedure and therefore is limited to only those subjects who are undergoing a surgical procedure.